SharePoint 2013: Product Configuration Wizard stuck on task 9 of 10

Problem

You have installed SP1 or some other cumulative update on all your farm servers without issue.  You then run the SharePoint Products Configuration Wizard on each machine.  It completes without issue on one or two machines, but then, on the next machine, it nearly completes but then appears to remain stuck on configuration task 9 of 10.  You wait an hour, but it still remains stuck on task 9 of 10.  You then check the Upgrade Status page in Central Administration

Solution

1. Delete the SharePoint Products Configuration Wizard dialog.  Terminate the process of necessary to remove it.
2. Open the Services.msc panel, and then look for the SharePoint Timer Service.
3. Stop this service.
4. Open Windows Explorer, and then navigate to the cache folder at: C:\ProgramData\Microsoft\SharePoint\Config.
5. Look for the most recent cache folder, and then open it.
6. Take note of how many configuration files are in this folder.  For example, looking in this folder for one of my WFEs, I see 1736, including the cache.ini.
7. Delete all files in this folder EXCEPT cache.ini.
8. Open the cache.ini file in a text editor, and then randomly modify the number, but keep it at the same number of digits.
9. Save the cache.ini file.
10. Start the SharePoint Timer Service.
11. Now watch the configuration folder.  It will start filling up with new configuration cache files quickly.  When it reaches the number you noted down in step 6, and you no longer see any new files being created, proceed to the next step.
12. Open a command prompt as Administrator.
13. Run the following command: Psconfig.exe -cmd upgrade -inplace b2b -wait -force
14. Check the Upgrade Status.

References

• Command-line reference for the SharePoint Products and Technologies Configuration Wizard (Office SharePoint Server)
• SharePoint 2013 Product configuration wizard failing at step 9/10
• sharepoint 2013 - After SP1 installation - Sharepoint products Configuration Wizard stuck

Notes

• Upgrade Status page: CA > Upgrade and Migration > Upgrade and Patch Management > Check upgrade status.
• Cache folder: You may get a Folder not found error trying to navigate to this folder.  If so, try navigating first to one of the higher tier folders, then double-clicking on each subfolder in turn.
• The path to psconfig is here: c:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\BIN\.
• Seems stuck on 10%: I've experienced this several times over the years.  Before determining that the upgrade process is actually experiencing problems, just do a simple check of the Upgrade log.  Check to see what the most recent time stamp is: if its quite recent then the upgrade process is likely moving forward successfully.  Check back again a moment later: if you see a new time stamp then again it is likely that the upgrade process is successfully moving forward and is just not updating the percentage complete in a meaningful way.  
• Actually stuck on 10%: then there is the case where you check back after awhile - maybe after a long while - and no new time stamp entry has been added to the Upgrade log - even after an hour or two.  In this case, there might be a problem.  Be sure to review the Upgrade error log to see if there are any unusual errors.  In this case, which I have experienced just once, fortunately.  This occurred during an upgrade launched by this command: PSConfig.exe -cmd upgrade -inplace b2b -force -cmd applicationcontent -install -cmd installfeatures.  Nothing unusual seemed to occur until it reached Step 5 of 6.  Checking the upgrade log found no issues; there was an upgrade error log generated, but the errors logged were the pesky "web application is configured with claims authentication mode however the content database you are trying to..." warnings that I ignore.  I waited an hour and then followed the procedure above, and I was able to successfully complete the upgrade. 
• Force upgrade to end with error: when it seems like the upgrade is stuck, you can force it to end, albeit with error, by stopping the timer and then restarting it.